1. Field of the Invention
The present invention relates to a photoradical generator comprising a compound comprising molecular structure having self-cleavage type radical-generating parts and ethylenic unsaturated groups, a photosensitive resin composition containing the generator, and an article produced from the resin composition.
Particularly, the invention relates firstly to a photoradical generator which itself has a function as a photoradical initiator and a function as a polymerizable compound and a self-cleavage type high reaction potential (high sensitivity) as well as fixation capability of the cleavage parts of the photoradical initiator in a matrix and is excellent in compatibility with monomer components.
Secondarily, the invention relates to a photosensitive resin composition containing the radical generator and being capable of decreasing the odor (outgas) at the time of exposure or post-baking and lessening volatile low molecular weight decomposition materials, particularly odorous components, remaining in a product after curing.
Thirdly, the invention relates to an article of which at least a portion is made of the cured product of the photosensitive resin composition and which has high heat resistance and stability so as to be scarcely deteriorated with heat.
2. Description of the Related Art
Photosensitive resins to be cured or to have solubility by light irradiation of UV rays or the like are generally classified into two types; those having exposed parts with good solubility (positive type) and those having unexposed parts with good solubility (negative type). In the case of the negative type, since the photosensitive resins themselves are cured and become insoluble by exposure, the photosensitive resins themselves often remain on substrates to from portions of products as functional films.
Although the negative type photosensitive resin has been used for, for example, paints, printing inks, overcoat layers, adhesives, printing master plates or the like, it has been recently used in wide applications ranging to products such as solder resists for wire protection in printed wiring boards, layer insulation films and resists for forming pixels in color filters, antireflection films, hologram or the like.
One of generally popular negative type photosensitive resins includes a resin composition containing a compound having one or more ethylenic unsaturated bonds, a photoradical initiator for generating radicals by light irradiation, and if necessary, a macro molecular compound, an inorganic filler, a pigment or the like for providing developing ability and softness of coating layer. When light is irradiated to the composition, the molecules of the compound having the ethylenic unsaturated bonds are bonded by radical reaction to increase the molecular weight and be cured. At the time of the curing reaction, three-dimensional mesh structure is developed by the crosslinking reaction, so that the hardness, strength, adhesion property, solvent resistance, and heat resistance of the cured product to be obtained are increased.
Photoradical initiators are broadly classified into self-cleavage type (Type I), and non-self-cleavage type (Type II) (Photocuring technology, p. 39, Technical Information Institute Co., Ltd., 2000). In the case of the former, just like a benzoin ether type compound, the bonds at the positions corresponding to light with specified wavelength are cut by absorbing the light and radicals are generated at the respective cut positions at the moment and there radical reaction starts. In the case of the latter, such a radical initiator has a radical generation mechanism for generating radicals without decomposition at the time of absorption of light with the specified wavelength and, for example, in the case of a hydrogen-drawing type represented by benzophenone, it absorbs electromagnetic wave with specified wavelength and when elevated to excited state, it draws hydrogen from hydrogen donors in the surrounding and at that moment, radicals are generated in both of the drawing side and the drawn side.
In general, self-cleavage type radical initiators are good in the sensitivity and radical generation efficiency, however generate low molecular decomposition materials at the time of light irradiation and such low molecular decomposition materials cause odor by volatilization in the work environments or are condensed again after volatilization to result in pollution of production apparatus and inferior product production, or such low molecular decomposition materials remain in products to deteriorate heat resistance and stability of the products or are slowly released from the products.
On the other hand, the hydrogen-drawing type are free from the generation or remaining of the low molecular decomposition materials derived from the initiators, however, they require existence of hydrogen donors in the vicinity of the excited initiators or have relatively low sensitivity since their radical generation efficiency is determined depending on the energy barrier height at the time of drawing of hydrogen.
To say more practically, there may be the following problems of the self-cleavage type initiators to be encountered in the case of various uses.
Firstly, as an example, use for a solder resist or color resist can be exemplified. The solder resist to be used for surface coverage of a printed wiring board contains an organic pigment and a filler for providing heat resistance and flame resistance or the resist for pixel formation for a color filter contains a pigment for color display. Since these pigments are components absorbing light, they utilize mainly self-cleavage type photoradical initiators and are added in large quantities including the amount for vain use in radical reaction of them Here, the portion which is not effectively used in the radical reaction includes the unreacted initiators not cleaved by radiation and those which become inactive by inhibition from the contact with objects to be reacted because of solid-phase reaction even though they become radical by cleavage.
Accordingly, the initiators are used in large quantities, so that large quantities of low molecular decomposition materials are generated at the time of light radiation and odor is emitted. Further, in the cured products after exposure, large quantities of residues derived from the initiators exist and among them, the un-self-cleaved photoradical initiators still keep reactivity even after the exposure and therefore denature the cured products. Also, the un-self-cleaved photoradical initiators and inactivated low molecular decomposition materials which are cleaved but not consumed by the radical reaction are not bonded to the crosslinking structure of the matrix and exist as independent components in the cured products to deteriorate the physical properties. Therefore, if the residues derived from the initiators are left as they are, they worsen the light fastness, colorization or discoloration, separation and cracking of the coating layers and lead to deterioration of the reliability of the final products, for example, interlayer insulating films for electronic parts, solder resist, resist for pixel formation for color filters.
The self-cleavage type photoradical initiator has a strong sublimation tendency and is decomposed by heat. It can be therefore removed from a product by post-baking after exposure and developing at a temperature higher than hundred and several tens degree. However, a large amount of a sublimated material originated from an initiator adheres to the inside of a heater and falls on a product obtained by curing during post-baking, causing product defects, posing a serious problem. Also, a decomposed material of an initiator or the like is involved in the atmosphere around the heater, posing a problem from the viewpoint of operational safety.
It is possible to remove more residues originated from a radical initiator by changing a post-baking condition to a condition of a higher-temperature and longer-operation time. However, it is difficult to remove the residues completely because of volatilization from a solid. If the condition is made stricter to remove many more impurities originated from a radical initiator, this condition rather causes product defects.
Secondary, use of resist for peeling films can be exemplified. Similarly to that of the above-mentioned solder resist, resist for processing electronic members, dry film resist or the like to be used for peeling films employ the photocuring system. The resists for processing are peeled and do not remain in the products finally, however, in the processing steps of copper wiring formation, the residues derived from the initiators from the resist films are eluted in chemical solutions such as ferric chloride, cupric chloride or the like to be used for the processing to shorten the chemical solution life.
Moreover, thirdly, use for coating material for protecting films can be exemplified. When a photosensitive resin is used as a wall used for buildings or paint for a protective layer protecting a surface of wall paper, there is a demand for decreasing solvent components or odorous components emitting from whole building material with the view of dealing with sick house syndrome. There is a problem that the use of a highly volatile initiator causes the occurrence of odors even after curing.
As one of the means for solving the above-mentioned problems, ESACURE KIP 150 (trade name) is commercialized by Nihon Siber Hegner K. K. The ESACURE KIP 150 has a structure in which photoradical generation portions are introduced in the side chains of the polymer skeleton. With such a structure, the photoradical generator has a plurality of radical generation portions in one molecule and therefore, if any one portion of the molecule is made radical and bonded with the matrix of the coating layer, the unreacted radical generation portions existing in the same molecule are bonded to the matrix structure and thus are not volatilized in post-baking and do not move in the coating layers to scarcely deteriorate the reliability of the final products.
However, ESACURE KIP 150 has a polymer skeleton with relatively large molecular size and therefore is difficult to move in a photosensitive resin composition. Further, the sensitive wavelength is not matched with the radiation wavelength of common light sources. Therefore, the sensitivity in the resin composition is not so high in practical use and the photoradical reactivity is hard to be increased.
As another solution, LUNA 750 (trade name) is commercialized by Nihon Siber Hegner K. K. The LUNA 750 is produced by introducing functional groups (side chains) with high molecular weight into self-cleavage type radical-generating parts having α-aminoacetophenone skeleton to increase the molecular weight of the parts to be isolated by cleavage at the time of radical generation and thus volatilization (outgas) of decomposition materials can be suppressed. However, in this case, the molecular weight in the cleaved parts is increased only to increase the temperature of the volatilization and make gasification difficult, the decomposition materials independent from the matrix structure of the coating layer remain in the coating layer. Therefore, it cannot sufficiently solve the problems of reliability deterioration, e.g. inferior products owing to the decomposition materials, occurrence of volatilization, elution, and odor emission of the decomposition materials, of the final products of coating layers or the like. Also, it cannot deal with the problem of elution of decomposition materials or unreacted materials derived from the initiators to developers or washing solutions in the case of development or washing intermediate products and final products.